Method of producing a corrosion



Reissued Aug. 26, 1952 MET-HOD- "or PRODUCING A ooRaosIoN RESISTANT COATING N STEEL Glenn H. McIntyre, Cleveland Heights, and Millard G. Ammon, Cleveland, Ohio No Drawing. Original No. 2,542,043, dated February 20, 1951, Serial No. 772,594, September 6, 1947. Application for reissue February 18, 1952,

Serial No. 272,274

, ZGlaims. (01. 14 -6) Matter enclosed in heavy brackets appears in the original patent but forms no part of this This invention relates as indicated to methods of producing corrosion resistant coatings, and

,more particularly to producing coatings for vide a method of producing a coating, characterized by the fact that the coating is extremely thin, very resistant to corrosion, while at the same time very tenaclously adherent to th underlying metallic article which may be formed of sheet steel.

Other objects of our invention will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, said invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following descriptionsetting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of th invention may be employed. r

Broadly stated, this invention comprises the discovery that very tenaciously adherent. corrosionresistant coatings may be providedon metallic articles, such as those made from sheet steel, by the application thereto of a porcelain enamel sheet steel ground coat which is applied much thinner than its normal weight of application when used as a ground coat,-and which, during the fusing state is very substantially over-fired so that the metallic oxides formed on the metallic surface during the initial stages of the firing operation are completely absorbed or dissolved by the coating which, in its final state, is preponderantly a layer of such oxides cemented. to the metallic surface by the residuum of th glass present in the enamel as applied.

metallic oxides" as a film onto the metallic surfaces to be, protected.

These prior art efforts have been generally unsatisfactory for various. reasons, amon which reissue specification; matter printed in italics indicates the additions made by reissue.

have been included high cost,th undesirable thickness of the coating necessaryto provide sufficient protection, and many times, as a result of the latter, very poor bond between the coating and the metalliclsurface. These prior-.art effortshave generally employed materials commonly known in the art as porcelain enamel cast iron ground coats for the reason that porcelain enamel ground coats as normally'applied ,to cast iron are generally loaded with very substantial amounts of relatively infusible materials such as silica and feldspar. Chromium oxide has also been used in very substantial quantities in prior art compositions with the undesirable results as above pointed out.

In contradistinction to these prior art attempts, We use coating compositions which, in the art, are generally known as porcelain enamel sheet steel ground coats. This class of ground coat enamels is characterized by the fact that they, as applied, consist substantially entirely of glass and are fired at a temperature, and under such conditions, that the components of the coating are substantially all completely fused. This is in contradistinction to the cast iron ground coat materials which, containing substantial quantities of raw materials such as feldspar, silica sand, and the like, are not reduced to a fused state.

' As an indication of the type of porcelain enamel sheet steel ground coats which may be used in carrying out our invention, reference may be had to the following table wherein will be found two specific examples and a range of representative compositions. I

Table A Parts By Weight Exailnple Exazmple Range Silica Sand 835 560 450 to 1, 000 Dehydrated Borax 684 634 500 to 850 760 800 650 to 850 206 262 150 to 40-) 138 120 to 200 Fluorspar 138 400 100 to 500 Cobalt Oxide-.. l6 17 up to 50 Manganese Oxide 34 34 up to 50 Black Nickel Oxide 2O 17 up to 50 Bone Ash up to 50 The materials given in the foregoing table are the raw batch composition. They, after being thoroughly mixed, may be smelted at about 2400 F., after which they are fritted by being run into a water bath. The enamel, slip for application to mam... I H...

posited on the work to a weight of about $6 to /4 oz. per square foot dry weight, preferably about.

/v oz. per square foot dry weight.

The enamel of Example 1 in Table A will provide a relatively hard glass, i. e., it will have a. somewhat higher firing temperature than the softer glass of Example 2. They will, however, usually fire out satisfactorily when used as a normal ground coat on sheet steel of about 20 gauge, at a temperature of. about 1560 to 1580 F. in a period of from. 3 to 5 minutes. We might say that when used as a normal ground coat, these enamels would be applied in weights of from 1% to- 1-% oz. per square foot dry weight as compared with. the preferred weights of application given above when practicing our improved process.

'After' the ground coat has been applied it will hefired at a'temp'erature of from about 1500 F. to about 1700' F. and preferably of from 1580 to 1600 F., i. e. slightly higher than the temperature at which it would be fired for normal ground coat use. The enamel will be fired preferably fora period of from 5 to 8 minutes, de-

pending upon the character of the enamel and the-nature of the workpiece, this it will be observed being approximately twice as long as the normal firing time as indicated above for normal" ground coat use.

Stated in another way, coatings when applied in accordance with our invention will be fired at a temperature of about 50-100 F. above the normalmaturing temperature of the coating and fora period of time approximately twice as long as thenormal firing time of the coating when used as a ground coat. When applying the coating to articles of different thickness, some allowance should be made for the thickness or weight of the base metal, as, for example, when applying the coating to a thin steel sheet the firing time need not be quite as long as when itis applied, for example, to a steel article of A inch thickness. The optimum firing conditionsfor thecoating may be expressed as those conditions substantially equivalent to those secured by" firing a gauge steel sheet for about 5-8 minutes at temperatures between 1500 and 1700 F.

The enamel is applied, of course, in its wet state. After drying, and during the initial stages of the firing operation, a certain amount of iron oxide is formed on the sheet steel surface being coated. The increase in firing time and temperature, is for a two-fold purpose: First, for,

thepurpose of developing the maximum amount of the oxide coating on the work; and second, and, of greatest importance, to completely dissolve or combine the metallic oxide coating with the glass of the applied coating, and to simultaneously fire down the glass to the point where his completely devitrified, and only just enough remains to serve as the medium to bond the iron oxide coating thus formed into a thin tenaciously adherent coating.

It? is a, characteristic of the coating that its color ischaracteristic of the color ofan oxide ofth'e' base metal" to which it is. applied; Thus, when applying the coating onto a steel sheet it .4 will be a reddish brown color characteristic of theox-ides of iron. q 1

A coating produced in this way is much superior to those produced in accordance with prior art eil'orts as above pointed out, for the reason that. forming the metallic oxide coating in situ on the work, simultaneous with the interfusion therewith of the glass, results in a coating which is. much more strongly adherent than those heretofore produced. The relatively thin weight of application of the glass leaves just enough glass as a residue to serve as the binder so, that the: corrosion-resistant coating is provided in the main by the metallic oxides thus formed.

While, in accordance with the preferred embodiment of our invention, the iron oxide for the coating; may thus beprovidedentirelyby an oxidation of the metallic surface, it is nevertheless possible to admix some iron oxide with the ground coat as applied, provided not too much isthus added; since any" increase in the amount" of ironends present, which is due to the additionof iron oxide to the coating, measurably decreasesthe adherence 6f the result ant film.

Other modes-of applyingthe principle or the invention may beemployed, change being made as regards the details described, provided the features stated in any of the followingclaims, or the equivalent oi" such, be employed;

We therefore" particularly point out and distinctly claim as our invention:

1. The method of coating a steel article which comprises applying on sucharticleacwting layer of fromabout {a to about ounce per-square foot dry weight, of afeldspar-silica borax coritainingiporcelain enaml'e'lsheet steel ground coat which when appliedat a dry weight of 1 A-v to 1% ounces er square foot would fuse to a glassy surface when fired on a 2 0 gauge steel sheet for about 3'- to' 5 minutes at a temperature of from about 1560" F. to"about- 158D" Fl, this tinteran e and this temperature range being-the" normal firing timeand the normal maturingtemperature when fusing said ground coat upon a steel sheet of about 20 gauge; then, while making allowance for the thickness or" weight of'the' steel if difler ing from Z'Ogauge, firing the coated article [at from about 5 teammates at from about 1500 I. to about 1700" Flat a'temperaturcof about 50 to F. above th'anormal maturing tem era;- ture of the; coating and for a period of timev approximately twice as longas' the normal firing time: of said ceatingwhen used as a ground coat, to first form: iron oxides" on the: metal surface and then to absorb such" oxides'into the" enamel coat to produce a substantially completely devitrified" coating, said; coating] being, characterized by its extreme" thinness, high resistance to corrosion and. tenacious adherence to the metal article. j

2. The'methofd of coatingja steel article. which comprises' applyingj' on such article a coating layer of such thickness that the. solid content thereof win weigh from. Te. to /4, ounce per square foot, the solid components of which are substa'ntia'll'y" entirely; glass which when applied at a dry weight of 1% to" 1% ounces perv square foot would fuse to a glassy surface whenlfired on a 20 gauge steeisheetlfor'fiif to sminutes" at a temperature of from" about I569? to about 1580 F., this time range dfld ifii's" temperature range being the normal firing tiinc arid the" normal maturing tem erature when fusing sa'iii ground coat upon a steel sheet of about 20 gauge, then, while making allowance for the thickness or weight of the steel if differing from 20 gauge, firing the coated article [at from about 5 to 8 minutes at from about 1500 to about 1700 F] at a temperature of about 50 to 100 F. above the normal maturing temperature of the coating and for a period of time approximately twice as long as the normal firing time of said coating when used as a ground coat, to form first iron oxides on the metal surface and then substantially to devitrify completely said glass components, said coating being characterized by its extreme thinness, a high resistance to corrosion and tenacious adherence to the metal article.

GLENN H. MCINTYRE. IMILLARD G. AMMON.

REFERENCES CITED The following references are of record in the file of this patent or the original patent:

UNITED STATES PATENTS 

